An underbite — where the lower teeth sit in front of the upper teeth — is a Class III relationship. Adults with an underbite often ask whether expansion can correct it. The honest answer is: it depends whether the underbite is dental or skeletal, and how severe the skeletal discrepancy is.
What Is It?
A dental underbite is caused by the position of the teeth within a normal skeletal framework. A skeletal underbite is caused by the jaws themselves: the lower jaw is too far forward, the upper jaw is too far back, or both. Expansion addresses the width of the upper jaw; it does not directly move the upper jaw forward.
Why Does It Matter?
Treating a skeletal problem with a dental solution leads to unstable, compromised results. Correctly diagnosing whether your underbite is dental, skeletal, or a combination is the single most important step before any treatment decision.
Diagnosis & Assessment
The decision is made on CBCT diagnosis. We assess the skeletal pattern, the amount of skeletal discrepancy, the suture and the soft-tissue profile, then recommend honestly whether expansion, expansion with protraction, or orthognathic surgery is most appropriate for you.
Benefits
- Expansion can help underbites with a transverse (width) component.
- Combined with protraction, it may contribute to limited forward movement.
- An honest diagnosis protects you from the wrong treatment.
Risks & Limitations
- Expansion alone cannot correct a true skeletal Class III discrepancy.
- Forward movement in adults is variable and cannot be guaranteed.
- Some cases require orthognathic surgery, which is a bigger commitment.
When expansion can help
If the upper jaw is narrow and the underbite has a transverse component, widening the maxilla with expansion can create space and improve the arch relationship. Where some forward movement of the upper jaw is also desired, expansion can be combined with protraction (for example BAMP), though the amount of forward movement in adults is variable and cannot be guaranteed.
When orthognathic surgery is the right option
If the underbite is a true skeletal Class III discrepancy — a significant mismatch between the upper and lower jaws — expansion and protraction alone will not correct it. In these cases, orthognathic surgery (jaw surgery) combined with orthodontics remains the appropriate and predictable option. This is not a failure of expansion; it is the correct treatment for a different problem. See our adult orthodontics page for more on combined orthodontic-surgical planning.
